1. Field
One or more embodiments described herein relate to storing data.
2. Description of the Related Art
A variety of semiconductor memory devices have been developed. Over the years, these devices have increased in terms of their integration and operating speed. For example, a dynamic random access memory (DRAM) has been used as a cache memory of a central processing unit (CPU) because of its integration scale and fast data writing or reading speeds. DRAMs have been used for this purpose even though they are volatile memories, e.g., ones in which stored data is lost when powered off.
A synchronous semiconductor memory device processes data using a clock signal. In order to increase bandwidth, a synchronous semiconductor memory device may operate in a double data rate (DDR) mode. In this mode, data is processed at rising and falling edges of the clock signal. A DDR memory device may therefore double bandwidth without increasing clock signal frequency. A DDR memory device may be controlled by a memory controller, which communicates with the DDR memory device and which may control transmission or reception of data in DDR mode.